Some of these standards are online & shared openly. Whist some like the Chinese standards can be paid/downloaded, yet others like Hong Kong MTR Design Standards, etc. are considered to be proprietary, only available for references by vendors who are designing these systems.
Hong Kong
Hong Kong MTR Design Standard Manual (Not available online).
Singapore.
Please note that the latest LTA's standards have changed, it is now controlled and not available for download. However, it is hard to see how the new Infrastructure Design Criteria (IDC) are substantially different?
GB 50157-2013 Subway Design Specifications (Design Standards)
GB 50226-2007 Code for design of railway passenger station buildings
GB 51298 Standard for Fire Protection, design of metro
Japan
Bang Kok
UK
Canada
US